Hi, 3 or 4 years ago I trained Judo. And Sumo was something else that the teacher teached for fun.
It's a lot of incredible fun. It's good to train your legs and your balance. It's more a sport than a martial art and it's awesome. I only have trained it for a year tho

Funny fact: When my former teacher traveled with the sumo team, Japan embassy payed him EVERYTHING, even the fancy dinners (yeah it's kind of a big deal for the japanese tradition).

Sumo is great. Tom Zabel is the head of the US Sumo Federation. Our gym is having him in for another practice this weekend. Practices can be pretty intense. I didn't realize what all went into it until I tried it and our judo/SAMBO club all really enjoy playing the sport. There are actually five upcoming events here in the states in the next few months. If you're interested in training sumo, reach out to Tom and he should be able to point you in the right direction.

We used to occasionally have little sumo bouts at my previous Judo club as kazushi awareness training. It was both fun and a helpful drill. But it doesn't really count as "training sumo". Just pointing out it's transference to other grappling.

If I recall Lyoto Machida's wrestling base is Sumo. He competed in it for a short while prior to his UFC career.